Who says covered up has to mean prim and proper? At the Paris premiere of her blockbuster film, “King Kong,” actress Naomi Watts smoldered in a long, lean black Rochas gown, made specially for her by designer Olivier Theyskens. With a high neckline, fishtail train and a judicious smattering of ruffles, the dress invoked the Edwardian silhouette Theyskens has favored in seasons past. But its sexy keyhole cutout and racerback guarantees this look isn’t for uptight governesses. Watts steered clear of period chic by accessorizing with sexy, kohl-rimmed eyes; smooth, unfussy hair; a chunky, gold-link David Yurman bracelet, and pull-on stretch and leather Rochas boots, which she gamely showed off to clamoring photographers by lifting her dress hem. Just like a modern girl would.